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(11) | EP 0 406 288 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
A METHOD FOR CONTINUOUS DRYING OF A MATERIAL VERFAHREN ZUR KONTINUIERLICHEN TROCKNUNG EINES MATERIALS PROCEDE DE SECHAGE EN CONTINU D'UN MATERIAU |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
Technical Field
[0001] The present invention relates to the use of a method for drying of a material, whereby:
a) the temperature of the material is adjusted to a value which is not injurious to the material;
b) the material is fed into a vacuum chamber,
c) the material is led through the vacuum chamber without any heat supply to the material, and
d) the dried material is removed from the vacuum chamber through an air lock.
Background Art
[0002] It is often difficult to remove the remaining water when preparing sugars or sugar alcohols which are sensitive as well as hygroscopic products in dry form, such as in powder form.
[0003] One of the reasons is the high content of hydrophilic groups in the above materials, rendering the products hygroscopic.
[0004] Another reason is the tendency of some of said materials to form supersaturated solutions, wherefrom it is difficult to precipitate and isolate solid products.
[0005] Supersaturated and other concentrated solutions are very often highly viscous. Consequently they are difficult to handle and have the tendency to stick to the apparatus.
[0006] All these properties further impede the removal of water, e.g. by evaporation or drying, since problems arise during the heating of the material. An equal distribution of heat is, for example, not ensured, thus risking local overheating. During the heating the material can be destroyed or deteriorate e.g. by burning, caramelization, denaturation or another form of decomposition.
[0007] Several methods for drying products in order to remove the remaining water are known, such as spray drying, drum drying, freeze drying or flash drying.
[0008] For spray drying, the solution to be dried is fed into a chamber in form of tiny drops. The falling drops are dried by means of hot air so that the drops are transformed into a dry powder before they reach the bottom of the chamber. Spray drying cannot be used if the solution has the tendency to remain liquid, either as an supersaturated solution or in form of a melt, during the drying process, where the temperature is usually above 60°C, since the material accumulates on the walls of the spray drying chamber.
[0009] Drum drying is normally performed at temperatures about 100°C. At this temperature many materials occur in form of a melt and thus they cannot be transformed into a solid product. During drum drying the product accumulates on the warm surfaces, causing overheating with subsequent destruction or deterioration of the material.
[0010] With conventional flash drying water is removed almost instantaneously from wet, solid particles, said particles being dispersed at high speed in a warm stream of gas. In flash drying the temperature of the drying air is above 100°C, rendering this drying method unsuitable for drying heat-sensitive products.
[0011] It is evident that neither spray drying, drum drying nor flash drying are suitable for the preparation of solid, dry products, such as some sugars and some sugar alcohols, other heat-sensitive products and/or those difficult to crystallize.
[0012] The only known methods suitable for drying such materials are freeze drying and microwave vacuum drying. These methods are, however, expensive, since their operational costs are high, especially with regard to energy consumption and capital costs.
[0013] The German Offenlegungsschrift No. 34 07 374 discloses a method for preparing dried products from sucrose syrup. According to this method the pre-concentrated sucrose syrup with a dry matter content of at least 70% is heated for a short period, such as below 60 sec, to a very high temperature, and the warm material is expanded to a concentrated syrup with a dry matter content of at least 90%. This syrup is transformed into a dry, pourable product by sudden cooling and subsequent release of the remaining water during crystallization.
[0014] This method is limited to easily crystallizable materials with a positive enthalpy of crystallization, i.e. materials crystallizing during cooling. The method is consequently unsuitable for the preparation of amorphous products and other materials difficult to crystallize. Furthermore the material is subjected to high temperatures of about 135-155°C, thus rendering the method unsuitable for heat-sensitive materials.
[0015] US-PS No. 1.250.496 discloses a process for drying grain and other coarse, granular materials, where the grain is heated and then subjected to first low vacuum and thereafter high vacuum. The process involves expensive equipment and the process cannot be used for drying particle-free, syrups.
[0016] US-PS No. 3.206.866 discloses a method and apparatus for dehydrating food employing geothermal steam. The food is fed into a vacuum chamber through an air lock and is transported through said chamber by means of several conveyor belts and is finally removed from the vacuum chamber through an air lock. The food is heated inside the vacuum chamber. The latter step renders this method unsuitable for dehydration of syrups since the material is locally overheated resulting in its deterioration.
[0017] US-PS No. 4.574.495 discloses a drying apparatus with a vacuum chamber, wherein the material to be dried is transported by means of conveyor belts. This apparatus is also equipped with means for supplying heat to the inside of the vacuum chamber. Therefore this apparatus also deteriorates a syrup due to overheating.
[0018] Finally EP Patent Application No. 0.231.584 A1 discloses a drying apparatus including a screw conveyor. The apparatus is heated by means of a heating mantle. Therefore also this apparatus is unsuitable for drying heat-sensitive materials, such as syrup-like material.
[0019] Other patents, such as SE-PS No. 342.896, SE-PS No. 374.811, US-PS 3.698.098 and US-PS No. 1.161.603, disclose various methods and apparatuses for drying materials, such as wood panels, protinaceous materials, heat-sensitive parachutes of synthetic fibres and colloid substances, respectively.
[0020] GB-PS No. 1.498.119 discloses a process for drying and expanding a paste, which is extruded into a vacuum chamber. The temperature of the paste is between 60 and 125°C. The known process is difficult to control, if the extruder aperture has a diameter of less than 0.25 mm. In order to effect an adequate control of the process the aperture should be of a diameter of from 0.5 to 5 mm.
[0021] DE-OS No. 2.744.099 discloses a method for preparing dextrose powder in dry form containing a major amount of β-dextrose anhydride. This method, however, involves a grafted crystallization and is not usable in case of non-crystallizing materials, such as a mixture of oligosaccharides prepared according to the concurrent DK patent application No. 1592/88, filed March 23, 1988.
[0022] P.E. Andersen and J. Risum (Introduktion til Levnedsmiddel-Teknologien, vol. 1, 3. edition, p. 333, 1982, Polyteknisk Forlag, Copenhagen) disclose a conventional flash evaporator. The evaporator is, however, only suitable for the preparation of concentrated, still liquid products.
Disclosure of the Invention
[0023] The object of the present invention is to find a useful method for removing the remaining water from heat-sensitive, hard or impossible to crystallize and/or hygroscopic syrups by drying such syrup with a high dry matter content. Said method avoids the above difficulties of the known methods and is less expensive than freeze drying and microwave vacuum drying.
[0024] Accordingly, the invention relates to the use of a method for continuous drying of a material, whereby
a) the temperature of the material is adjusted to a value below the boiling point of said material at atmospheric pressure,
b) the material is fed into a vacuum chamber,
c) the material is led through the vacuum chamber without any heat supply to the material, and
d) the dried material is removed from the vacuum chamber through an air lock,
which use is characterised in that the material is a substantially particle-free syrup selected from the group consisting of syrups of carbohydrate and syrups of sugar alcohol, and that the temperature of said syrup in step a) is adjusted to a value below the boiling point of said material at atmospheric pressure but sufficiently high for the material to be dried in step c) to an amorphous solid product.[0025] The previously mentioned methods known from GB patent No. 1,498,119 and US patent No. 1,250,496, respectively, share substantial points of resemblance with the method used according to the invention. However, the known methods are used for the drying of another type of material, such as extracts of coffee, chicory and other coffee substitutes, tea and herbal extracts which are extruded as powder or paste in the former and grain in the latter of the known methods. It is thus a question of another type of starting material than those dried by the method used according to the invention where such are used as starting material which may especially be defined as particle-free syrups of carbohydrate and/or sugar alcohol. All the examples of the above GB patent relate to products which have already been freeze dried or spray dried. By the known drying processes it is thus not a question of a phase shift from a liquid to a solid product. According to the above GB patent, the drying product is disintegrated before it has finished expanding. By the method used according to the invention, the expansion takes place momentarily after the dosing. The product is not subjected to the optional coarse grinding until after the drying.
[0026] Although it is known to carry out a continuous drying of a material where
a) the temperature of the material is adjusted to a value which is not injurious to the material,
b) the material is fed into a vacuum chamber,
c) the material is led through the vacuum chamber without heat being supplied to the material, and
c) the dried material is removed from the vacuum chamber through an air lock,
it is new to use such method for continuous drying of a substantially particle-free syrup of carbonhydrate and/or sugar alcohol, where the temperature of the syrup in step a) is adjusted to a value below the boiling point of the material at atmospheric pressure and where an amorphous, solid product is formed by the drying.[0027] The person skilled in the art has not previously thought about using a method having the above known features for drying of syrups per se, that is such materials which are hygroscopic and which tend to form oversaturated solutions which are highly viscous and therefore difficult to handle and which tend to adhere to the apparatus used. Materials which are difficult to crystallize pose special problems.
[0028] The present invention was originally the result of the efforts to solve the task of drying the mixture of inulides, which is described in Applicant's Danish patent application No. 1592/88, as this mixture proved especially difficult to work with, as a solid product cannot be formed by crystallization, as is the case with a syrup of saccharose.
[0029] To solve such task, the person skilled in the art would traditionally look for a corresponding known method and the most obvious method would be the method used for drying fruit syrups. When such fruit syrups are to be dried, maltodextrin is conventionsally added, as this permits spray drying of the syrup. This solution is, however, not particularly attractive as products are obtained having a content of up to 50% maltodextrin, which must be considered an unwanted filler. Thus, if this known method for drying of the above inulin mixture was used, the product obtained would be less sweet and it would possess less body.
[0030] As according to prior art, drying of the type of syrups dealt with here has not previously been carried out, the person skilled in the art could not know whether the method was practicable without encountering severe problems with deposits on the walls of the vacuum chamber which would make it impossible to solve the task in practice. However, it has been found that the method known from drying of for instance pasta-like products may advantageously be used for these particularly difficult syrups and, surprisingly, it has been found that as a result, a product is obtained which has particularly excellent properties, as the product is an amorphous solid product.
[0031] Although the inventive use has been developed to dry the above particularly difficult mixture of inulides, it has also proved suitable for drying crystallizable types of sugar, e.g. saccharose. By using the method for such starting materials, the end product prepared would deviate from the product obtained by the conventional crystallization method. Thus, the product prepared by the inventive use has a special amorphous structure which makes the product suitable for forming agglomerates. Such agglomerates are advantageous. They are very easy to mix with other, they have an improved flowability, are less dusty and display a lesser tendency to absorb moisture from the atmosphere. Furthermore. it is possible to obtain agglomerated products with a high bulk density.
[0032] The resulting special structure has very special functional properties which, in addition to the above, also include an aroma-carrying effect. The desirable properties of the amorphous structures of types of sugar are described in an article by E.A. Niediek: "Effect of Processing on the Physical State and Aroma Sorption Properties of Carbohydrates". In said article, Niediek reaches the conclusion: "Economical methods for the precise production of amorphous substances do not exist yet. However, once they are developed, amorphous substances will find a large market because of their many desirable functional properties". It appears from this conclusion that the present invention will supply a large demand on the market.
[0033] The product obtained by the method has a particular amorphous structure rendering it suitable to form agglomerates. Such agglomerates are advantageous because they are very easily admixed other materials. Compared to crystalline products they have a better flowability due to their smaller surface, a smaller amount of dust and display a lesser tendency to absorb humidity from the atmosphere. Furthermore it is possible to obtain agglomerate products having a high bulk density.
[0034] Furthermore solid and non-tacky materials having a dry matter content of only 95% by weight can be prepared by the method.
[0035] The starting material of the method is a material concentrated by means of conventional methods, e.g. evaporation. The degree of concentration depends on the material, since the danger of destruction or deterioration, energy consumption and rheologic properties of the concentrate have to be taken into consideration.
[0036] The method normally removes 2-9% by weight of water based on the feed. This is, for example, used for drying an oligosaccharide with a dry matter content of 91-95% by weight into a powder with a dry matter content of 95-99% by weight.
[0037] The method is suitable for drying a mixture of oligosaccharides with a general formula GFn, wherein G is glucose, F is fructose and n is an integer, said mixture being further described in the concurrent patent application DK Patent Application No. 1592/88 and comprising 10-20% weight of G + F + GF, 10-20% by weight of GF₂, 8-15% by weight of GF₃ and 72-45% by weight of GF₄ and above.
[0038] This mixture is obtained from plant tubers or roots, especially the tubers of the Jerusalem artichoke, Helianthus tuberosus L. or roots of chicory, Cichorium, using a conventional plant for treating sugar beets to prepare a syrup of a dry matter content of 65-80% by weight. This syrup is further evaporated by means of a suitable evaporator, such as a falling film evaporator, a vertical vacuum dryer and a thin film evaporator, to a dry matter content of 91-95% by weight before it is subjected to the inventive method. The material is removed from the evaporator at a temperature of 80-100°C. It is necessary to maintain this temperature, since otherwise the material turns viscous and thus accumulates on the walls of the evaporator, resulting in an interruption of its operation and destruction of the product.
[0039] For the method the temperature of the material is adjusted to a value below its boiling point. The enthalpy of the material is such that no heat supply is necessary during the subsequent steps (b, c and d).
[0040] The material is then fed into a vacuum chamber, preferably by distributing it corresponding to a thin layer, in dropform, or in any other way ensuring a large surface of the material.
[0042] When the material has entered the vacumm chamber the boiling point of the material is lower than the temperature of the material at the pressure in the vacuum chamber, causing a spontaneous evaporation of water. The heat of evaporation of water is taken from the material resulting in a corresponding drop in temperature. It is thus unnecessary to supply external heat. Supplying external heat during evaporation would cause undesired local overheating. In the present case external supply is avoided thus simplifying the process and reducing the costs for the equipment. Furthermore, the material is hot while it has the highest water content.
[0043] During the evaporation of water in a vacuum chamber the material is cooled down to a temperature slightly above the temperature where the vapor pressure of water corresponds to the absolute pressure in the vacuum chamber. The vapor pressure of water at 22, 25, 30, 35 and 38°C is 19.8, 23.8, 31.8, 42.2 and 49.7 mmHg respectively. When the vacuum chamber has an absolute pressure of 23.8 mmHg the product leaves the vacuum chamber due to boiling point elevation with a temperature of approx. 27-30°C, while an absolute pressure of 42.2 mmHg results in a temperature of 37-40°C.
[0044] The dry and cold product is removed from the vacuum chamber through an air lock, e.g. a cell air lock, ensuring a continuous running of the assembly.
[0045] This way of drying is just as gentle as freeze drying, but considerably less expensive. In case of the above mixture on the basis of tubers of Jerusalem artichokes, described in the concurrent Danish Patent Application No. 1592/88, the energy costs for concentrating the material from a dry matter content of 66% by weight to 98-99% by weight are 0.80 DKK/kg when freeze-drying is used. In comparison the total energy costs for concentrating the same material in three steps comprising the inventive method, i.e. from 66% by weight to 85% by weight in a falling film evaporator, from 85% by weight to 92% by weight by means of batch evaporation in a vertical vacuum dryer and from 92% by weight to 98-99% by weight according to the inventive method are only 0.11 DKK/kg.
[0046] When drying a syrup of a dry matter content of 91-95% by weight the temperature of the syrup is adjusted to 80-100°C, preferably 90-100°C. This is advantageously achieved by maintaining the temperature of the syrup leaving the pre-evaporation step.
[0047] The absolute pressure in the vacuum chamber is kept at 10-60 mmHg, preferably 20-50 mmHg. The material is carried through the chamber by a means of transport or by free fall and leaves the vacuum chamber through an air lock, optionally subsequent to grinding. The powder obtained in this manner is of a dry matter content of 95-99% by weight and its temperature has dropped to 25-40°C.
[0048] For setting a suitable duration time in the chamber the velocity of the means of transport is preferably adjustable or controlable. The basis for such a control is e.g. the dry matter content of the finished product, the temperature of the product when leaving the air lock or other values.
[0049] For the method to be carried out in a suitable and reliable manner the following data has to be in a matching, dynamic balance:
- composition of the starting material, incl. its water content,
- flow rate of the starting material,
- temperature of the starting material,
- pressure in the vacuum chamber,
- transport velocity through the chamber and
- temperature and dry matter content of the finished product when leaving the vacuum chamber.
[0050] In order to ensure such a dynamic balance the method is preferably carried out in the following way:
a) the temperature of the material is adjusted to a temperature less than 30°C below the boiling point of the material, preferably less than 10°C below the boiling point,
b) the material is fed into a vacuum chamber having an absolut pressure of 10-60 mmHg,
c) the material is led through the vacuum chamber by a means of transport,
d) the dried material is removed from the vacuum chamber through an air lock, optionally subsequent to a preceding gross grinding.
[0051] In order to obtain a suitable flow of the material through the vacuum chamber, the velocity of the means of transport is advantageously adjustable.
[0052] In an alternative, preferred embodiment also ensuring the above dynamic balance
a) the temperature of the material is adjusted to a temperature less than 30°C below the boiling point of the material, preferably less than 10°C below the boiling point,
b) the material is fed into a vacuum chamber having an absolut pressure of 10-60 mmHg,
c) the material is led through the vacuum chamber by means of free fall,
d) the dried material is removed from the vacuum chamber through an air lock, optionally subsequent to a preceding gross grinding.
[0053] For obtaining a suitable dry matter content of the powder the material fed into the vacuum chamber is advantageously of a dry matter content of 91-95% by weight.
[0054] The method is especially suitable for drying of materials, such as syrups comprising carbohydrates; syrups comprising sugar alcohol; honey; fruit juices and vegetable juices. Accordingly the method is potentially suitable for drying e.g. invert syrup, isosyrup (high fructose syrup, HFCS), enriched high fructose syrup (EFCS) and glucose syrup; sorbitol and xylitol; vegetable and fruit juices, such as carrot juice, tomato juice or apple juice; and the above mixture of saccharides mentioned in the concurrent DK Patent Application No. 1592/88.
[0055] Examples of the composition of the above HFCS and EFCS are:
| HFCS: | 42% by weight of fructose |
| 5% by weight of higher sugars | |
| 53% by weight of glucose | |
| EFCS: | 55% by weight of fructose |
| 5% by weight of higher sugars | |
| 40% by weight of glucose |
[0056] For ensuring a substantially complete and fast evaporation of water the means of transport is advantageously a conveyor belt and the material is distributed on the conveyor belt in an amount corresponding to a layer with a thickness of 1-10 mm, preferably 2-5 mm. Such a layer is, however, never formed in practice, since the material foams up immediately upon entering the vacuum chamber.
[0057] Excellent transport characteristics are alternatively achieved by employing a screw conveyor. The screw conveyor is preferably a self-cleaning twin screw to prevent the accumulation of material on the screw. A suitable fast transportation rate of the material through the vacuum chamber is obtained by employing several screws, for example 2-6 and preferably 2-5, said screws being parallel and adjacent to each other.
[0058] When 2 or more screws are used they can rotate in the same or opposite direction, as righthanded as well as lefthanded screws may be used.
[0059] According to the invention the use of the method can be carried out by means of an assembly characterized in that it comprises a means for adjusting the temperature of the material to a value below the boiling point of the material at atmospheric pressure, a feeding means for feeding the material into a vacuum chamber, a vacuum chamber, a means of transport for carrying the material through the vacuum chamber, and an air lock.
[0060] In one embodiment of the assembly the means of transport is a conveyor belt made of e.g. steel, plastic, rubber or other suitable material.
[0061] The feeding means is provided with a device for distributing the material by means of extrusion on the conveyor as a layer, preferably corresponding to a thickness of 1-10 mm, more preferred 2-5 mm. As mentioned this layer is only formed theoretically, in practice the material immediately foams up. During transport through the vacuum chamber the material thus foams up, as the water evaporates fast, causing an immediate drop in temperature. At the end of the conveyor belt a knife or scraper scrapes the dried material off the conveyor belt, whereupon it falls into a screw conveyor.
[0062] The screw conveyor - also under vacuum - crushes the product and transports it to an air lock, such as a cell air lock, wherefrom the dried product is continously removed in form of a powder. The crushing also ensures that the product is able to pass through the air lock.
[0063] In an alternative embodiment of the assembly the means of transport is formed like a screw conveyor, e.g. a twin-screw conveyor. In this embodiment the material is fed onto the screw through an extruder or by spraying it through a nozzle, and carried towards the output side by the screw. The material is distributed corresponding to a thin layer on the surface of the screw, said layer instantaneously foaming up by the sudden evaporation of water. The resulting foam is crushed and ground by the screw in such a way as to enable the dried product to fall into a hopper at the output side to be removed through an air lock, preferably a cell air lock.
[0064] If the product is very sticky, as is the case of many syrups, the screw is advantageously a self-cleaning screw. A self-cleaning twin screw includes two screws, one of them rotating twice as fast as and having a pitch half a large as the other one. The self-cleaning screw is provided with a self-cleaning rounded section so that the two screws clean each other. Usually there is a gap of 3 mm between the two screws, for especially fine processing, however, the self-cleaning twin screw can be manufactured with a gap of down to about 1 mm.
[0065] In both embodiments the amount of material to be fed and the velocity or speed of the belt or screw are determined in such a way that the layer theoretically formed on the belt or screw is sufficiently thin.
[0066] It is thus advantageous to render the velocity or speed of the belt or screw adjustable or controlable.
[0067] In a further embodiment the means for carrying the material through the vacuum chamber is provided by free fall. This assembly is especially suitable for drying sticky materials difficult to remove from the means of transport. This embodiment constitutes a simple and inexpensive alternative to the self-cleaning screw.
[0068] An assembly according to this embodiment suitably comprises a means for adjusting the temperature of the material to a value below the boiling point of the material at atmospheric pressure; a feeding means for feeding the material through apertures into the top of the vacuum chamber; a vacuum chamber provided for free fall; a hopper at the bottom of the vacuum chamber for collecting the dried material; a beater situated inside the hopper and an air lock.
[0070] In all above embodiments the feeding means is preferably provided with several apertures or one or more narrow gaps or slots, the most narrow dimension of said apertures, gaps or slots being not more than 2 mm, preferably not more than 1 mm, most preferably not more than 0.25 mm. The narrow dimension ensures a good distribution of the material throughout the vacuum chamber as well as a short drying period.
[0071] Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Brief Description of the Drawings
[0072] The invention is explained below in greater detail and with reference to the accompanying drawings, in which
Fig. 1 shows a first embodiment of the assembly, where the means of transport is a conveyor belt, and
Fig. 2 shows another embodiment of the assembly where the means of transport is a twin-screw conveyor.
Fig. 3 shows the relation between the dry matter content of the starting material and the material leaving the assembly and the temperature by means of the method when flash drying glucose syrup as described in Example 8.
Fig. 4 shows a third embodiment of the assembly using free fall as a means of transport.
Best Mode for Carrying out the Invention
[0073] Fig. 1 illustrates a vacuum chamber 2 inside a housing 4. To resist the external pressure the housing 4 has the shape of a cylinder with convex ends. The vacuum chamber 2 is connected to a vacuum source (not shown) via a connection piece 6 and corresponding channels (not shown). The vacuum pump is preferably a water ring vacuum pump. Between the vacuum pump and the vacuum chamber a condenser can be installed, where the steam from the vacuum chamber condensates. The installation of a condenser increases the efficiency of the vacuum pump. The material to be dried is fed into a channel 8 connected to a distributing piece 10. The distributing piece 10 can be provided with several small apertures or one or more small gaps or slots, said apertures, gaps or slots optionally being of varying length or width. The distributing piece distributes the material in a uniform amount across the entire width of the distributing piece.
[0074] A conveyor belt 12 runs on two rolls 14 with adjustable speed. The distributing piece 10 distributes the material over one end of the conveyor belt 12. By choosing a suitable adjustment of the feeding rate through the channel 8 and the distributing piece 10 and of the velocity of the conveyor belt 12 the material is distributed across the width of the conveyor belt 12 in an amount corresponding to a uniform, thin layer. During the transport through the vacuum chamber 2 water evaporates from the material 16 and the material foams up. When it has reached the opposite end of the conveyor belt 12 the material has been converted into a dry and solid product and is scraped off by a scraper 18.
[0075] The scraped-off product falls into a screw 20 in a chamber 22. The chamber 22 is connected to the vacuum chamber 2 and is thus also exposed to vacuum.
[0076] The screw 20 transports the product to a cell air lock 24, simultaneously crushing and grinding said product. The finished product 26 is removed through the air lock 24.
[0077] Fig. 2 shows an alternative embodiment of the assembly. A vacuum chamber 102 is inside a housing 104 of cylindric shape with convex ends as in the embodiment of Fig. 1. The vacuum chamber 102 is connected to a vacuum source via a connection piece 106 and channels (not shown). The material is fed through a channel 108 directly to the input end of a speed-adjustable twin screw 112. The material feeding rate through the channel 108 and the speed of the twin screw 112 is adjustable as to allow the material to be distributed corresponding to a thin and uniform layer on the surfaces of the twin screw 112. During transport through the vacuum chamber 102 water evaporates from the material 116 and the material foams up. Simultaneously, the twin screw crushes and grinds the material. As a result, the material reaches the output end of the twin screw as a dry, pulverized product. The product falls directly into a cell air lock 124, optionally by employing an internal funnel. The finished product 126 is removed through the air lock 124.
[0078] Fig. 4 shows an alternative embodiment of the assembly. A vacuum chamber 202 inside a housing is connected to a vacuum pump 205 via a connection piece 206. The material is fed to a distributing piece 210 via a channel 208. The distributing piece 210 has one or more small apertures for instance having a diameter of 1 mm. The dried material falls into a hopper 211, wherein a beater 213 disintegrates the dried material. The disintegration allows the removal of the material through a ball valve 215. When the ball valve is filled it is turned 180° and the finished product 226 is removed. The ball valve 215 is provided with a suction conduit to the vacuum pump 205 ensuring that no air leaks into the vacuum chamber when returning the ball valve 215. Between the vacuum pump 205 and the vacuum chamber 202 a condenser 228 is installed, said condenser being fed with cooling water 230. The steam from the vacuum chamber is condensated in the condenser 228 thus increasing the efficiency of the vacuum pump.
[0079] The invention is described below in greater detail by means of the following examples. Example 1 describes the preparation of the starting material, while Examples 2-10 describe the method used according to the invention.
Example 1: Preparation of a syrup.
[0080] The harvested tubers of the Jerusalem artichoke are treated on a conventional plant for treating sugar beets. The treatment includes the following steps.
1. Feeding and removal of stones and grass
[0081] The tubers are emptied into a beet yard and flow into the plant, while stones as well as green plant material (i.e. grass and stem material) are removed. Most of the soil is also washed off.
2. Cutting
[0082] For preparing the tubers for to the subsequent extraction process said tubers are cut into cosettes with a cross-section of approx. 0.5 x 0.5 cm. Their length depends on the size of the tubers (typically 2-5 cm). The cutting process is performed on a conventional sugar beet cutter. It can, however, be necessary to use other knives.
3. Extraction
[0083] In order to extract the desired product from the cosettes, the extraction process is performed analogous to the one known from the extraction of sugar from sugar beets. The extraction is performed in a so-called DDS-diffusor, a trough with a steam mantle. The trough has a small inclination and is provided with a twin screw ensuring transport of the cosettes.
[0084] The cosettes are extracted according to the counterflow principle, i.e. the cosettes are fed through a funnel in the bottom part of the trough. Water as well as the press juice obtained in step 4 are fed into the top part of the trough.
[0085] The cosettes are then transported counter to the flow of water, whereby oligosaccharides and other water-soluble components, such as salts and proteins, pass into the water phase.
[0086] The temperature during the extraction is between 60-85°C. Such a high temperature ensures not only a good solubility of oligosaccharides but also partially denaturates the protein as to render it insoluble. Enzymes are also denaturated and thus inactivated at this temperature.
4. Pressing of the pulp
[0088] The extracted cosettes are pressed in a special press of the type also used for conventional sugar beet processing. This is done to increase both the yield of oligosaccharides as well as the dry matter content of the pulp. The pulp has often to be dried with regard to stability during transport and storage until use, e.g. in form of foodstuffs. The increase in yield is achieved by transferring the press juice back to the extraction process, as described above.
5. Purification of the juice
[0089] The juice obtained by the extraction process is turbid since it contains particulate and colloidal material. Amongst the impurities present are pectin and proteins as well as cell material from the cosettes.
[0090] In order to remove these impurities slaked lime, Ca(OH)₂ is added up to a pH-value of 10.5-11.5, thereby precipitating a part of the impurities.
[0091] The pH-value is lowered again by adding CO₂ or phosphoric acid either before or after filtration. Thus excess calcium is precipitated either as calcium carbonate or calcium phosphate. The pH-value after this treatment is between 8.0 and 9.5. The juice is subsequently filtered. The temperature during the lime treatment is 35-40°C, and during the lowering of the pH-value and the filtering it is 60-80°C. Precipitation and filtering are improved at the higher temperature.
[0092] The purification of the juice is performed using the same equipment as in conventional sugar beet processing.
6. Ion exchange
[0094] After the purification the juice still contains salts (3-8% by weight of the total dry matter) and it is brownish or greenish in colour. It is thus subjected to a cation as well as an anion exchange.
[0095] The cation exchange (e.g. on a "DuoliteR"-C20 resin) is performed at a temperature of 25-35°C in order to avoid hydrolysis of the oligosaccharides.
[0096] During the anion exchange (e.g. on a "DuoliteR" A-378 resin) the coloured compounds of the juice are also removed as to render said juice a colourless oligosaccharide solution. The dry matter content after the ion exchange is 8-14% by weight.
7. Treatment with active carbon
[0097] It may necessary to treat the ion-exchanged juice with active carbon in order to remove possible residues of coloured compounds, undesired taste or odoriferous compounds.
8. Evaporation
[0098] Before the actual evaporation it is advantageous to employ hyperfiltration (reverse osmosis) in order to remove part of the water so that the dry matter content is up to approx. 25% by weight. By this step a more gentle treatment is obtained.
[0099] The evaporation is performed in a multi-step evaporator such as a falling film evaporator. The juice is evaporated to a syrup of a dry matter content of between 75-85% by weight.
[0100] Thereafter the syrup is evaporated in a vertical vacuum dryer or a thin film evaporator to a dry matter content of 90-96% by weight, preferably 91-93% by weight.
Example 2: Vacuum flash drying
[0101] A syrup having a dry matter content of 91-93% by weight obtained according to the method of Example 1 and being of a temperature of 80-100°C is transferred to a vacuum chamber provided with a conveyor belt.
[0102] By adjusting the dry matter content and the temperature of the feeding material as well as the vacuum in the chamber the obtained product has a temperature of 30-40°C after evaporation of water and is solid. The heat of evaporation is derived from the enthalpy of the feeding material, i.e. it is not necessary to add heat during the drying process.
[0103] At an absolute pressure of 23.8 or 42.2 mmHg the product leaving the vacuum chamber has a temperature of approx. 30°C or approx. 40°C respectively.
[0104] The process can be described as a flash-like evaporation in vacuum, the feed being a syrup and the final product a dry powder.
[0105] The above process differs from conventional flash evaporation by being performed in vacuum, thus rendering it unnecessary to overheat the feeding material, and by the feeding material being a solution and not a wet, particulate matter.
[0106] An interesting property of this drying method is the fact that the product is cooled to a desired final temperature of typically 30-40°C during the drying/water evaporation.
Example 3
[0108] The general procedure described in Example 2 is carried out in a vacuum chamber provided with a self-cleaning twin screw. In this way a final dry powder product similar to the product obtained in Example 2 is obtained.
Example 4
[0109] A syrup having a dry matter content of 91% by weight and a temperature of 95°C obtained according to Example 1 is fed into a vacuum chamber provided with a conveyor belt. The absolute pressure in the vacuum chamber is 25 mm Hg. The dry powder leaving the chamber has a dry matter content of 96% by weight and a temperature of 31°C.
Example 5
[0110] A syrup having a dry matter content of 93% by weight and a temperature of 95°C obtained according to Example 1 is fed into a vacuum chamber provided with a conveyor belt. The absolute pressure in the vacuum chamber is 39 mm Hg. The dry powder leaving the chamber has a dry matter content of 98% by weight and a temperature of 39°C.
Example 6
[0111] A syrup having a dry matter content of 92% by weight and a temperature of 85°C obtained according to Example 1 is fed into a vacuum chamber provided with a conveyor belt. The absolute pressure in the vacuum chamber is 30 mm Hg. The dry powder leaving the chamber has a dry matter content of 95.8% by weight and a temperature of 35°C.
Example 7
[0112] A syrup having a dry matter content of 91% by weight and a temperature of 99°C obtained according to Example 1 is fed into a vacuum chamber provided with a self-cleaning twin screw. The absolute pressure in the vacuum chamber is 30 mm Hg. The dry powder leaving the chamber has a dry matter content of 96.5% by weight and a temperature of 35°C.
Example 8: Drying of glucose syrup
[0113] The starting material is a commercially available glucose syrup with a dry matter content of 80% by weight. The syrup is pre-evaporated by means of batch evaporation for 2 h in a vertical vacuum dryer to a dry matter content of 92.5% by weight. During the evaporation the syrup has a temperature of 85°C and the vacuum is 80% (absolute pressure about 150 mm Hg). After the batch evaporation the temperature is elevated to 95°C and the syrup is extruded into a vacuum flash dryer, as shown in Fig. 1. The gap of the extruder has a width of 0.5 mm. In the vacuum flash dryer the absolute pressure is 24 mm Hg.
[0114] After leaving the extruder the syrup foams up momentarily to a thickness of 5-6 cm. After a sojourn time of 1 1/2 min the dried syrup leaves the vacuum flash dryer at a temperature of 35°C in form of a rough granulate with a dry matter content of 97.5% by weight.
[0115] Fig. 3 is a diagram illustrating the possibilities of altering the dry matter content and the temperature of the input material and still end up with the same final product. In Fig. 3 the abscissa represents % by weight of the dry matter content in the input material and the ordinate represents the dry matter content in % by weight of the material leaving the assembly.
Example 9
[0116] A mixture comprising 80% by weight of glucose syrup having a dry matter content of 80% by weight and 20% by weight of concentrated apple juice having a dry matter content of 67% by weight is evaporated in a vertical vacuum dryer to a dry matter content of 92.5% by weight. After the evaporation the temperature is adjusted to 97°C and the material is extruded through nozzles having a diameter of 1 mm into a vacuum flash dryer with free fall as shown in Fig. 4. In the vacuum flash dryer the absolute pressure is 10 mm Hg. The dry powder leaving the vacuum flash dryer has a dry matter content of 96.3% by weight and a temperature of about 34°C.
Example 10
[0117] In a vertical vacuum dryer cane sugar molasses having a dry matter content of 80% by weight is evaporated to a dry matter content of 93% by weight, whereupon the temperature of the material is adjusted to 96°C. The molasses is extruded into the vacuum flash dryer of Example 9, the absolute pressure in said dryer being 14 mm Hg. A dry amorphous powder leaving the vacuum flash dryer has a dry matter content of 96.3% by weight and a temperature of about 32°C.
1. The use of a method for the continuous drying of a material, whereby:
a) the temperature of the material is adjusted to a value which is not injurious to the material;
b) the material is fed into a vacuum chamber,
c) the material is led through the vacuum chamber without any heat supply to the material, and
d) the dried material is removed from the vacuum chamber through an air lock.
characterised in that the material is a substantially particle-free syrup selected from the group consisting of syrups of carbohydrate and syrups of sugar alcohol, and that the temperature of said syrup in step a) is adjusted to a value below the boiling point of said material at atmospheric pressure, but sufficiently high for the material to be dried in step c) to an amorphous solid product.2. The use as in claim 1, characterized in that the temperature of the material in step a) is adjusted to a temperature less
than 30°C below the boiling point of the material, preferably less than 10°C below
the boiling point, that the material in step b) is fed into a vacuum chamber having
an absolut pressure of 10-60 mmHg, that the material of step c) is led through the
vacuum chamber by a means of transport and that the dried material optionally is gross
grinded before it is removed from the vacuum chamber through an air lock in step d).
3. The use as in claim 2, characterized in that the velocity of the means of transport is adjustable.
4. The use as in claim 1, characterized in that the temperature of the material in step a) is adjusted to a temperature less
than 30°C below the boiling point of the material, preferably less than 10°C below
the boiling point, that the material in step b) is fed into a vacuum chamber having
an absolut pressure of 10-60 mmHg, that the material in step c) is led through the
vacuum chamber by means of free fall and that the dried material is optionally gross
grinded before it is removed from the vacuum chamber through an air lock in step d).
5. The use as in claim 1, characterized in that the material fed into the vacuum chamber is of a dry matter content of 91-95%
by weight.
1. Verwendung eines Verfahrens für die kontinuierliche Trocknung eines Materials, wobei:
a) die Temperatur des Materials auf einen Wert eingestellt wird, der für das Material nicht schädlich ist;
b) das Material in eine Vakuumkammer eingeführt wird;
c) das Material ohne jede Wärmezufuhr auf das Material durch die Vakuumkammer geführt wird; und
d) das getrocknete Material aus der Vakuumkammer durch eine Luftschleuse entfernt wird;
dadurch gekennzeichnet, daß das Material ein aus der aus Kohlehydratsirupen und Zuckeralkoholsirupen bestehenden Gruppe ausgewählter, im wesentlichen partikelfreier Sirup ist, und daß die Temperatur des Sirups im Schritt a) auf einen Wert unterhalb des Siedepunkts des Materials bei Athmosphärendruck eingestellt wird, die aber ausreichend hoch ist, daß das Material im Schritt c) zu einem amorphen festen Produkt getrocknet wird.2. Verwendung nach Anspruch 1, dadurch gekennzeichnet, daß die Temperatur des Materials
im Schritt a) auf eine Temperatur von weniger als 30°C unterhalb des Siedepunkts des
Materials eingestellt wird, vorzugsweise weniger als 10°C unter dem Siedepunkt, daß
das Material im Schritt b) in eine Vakuumkammer mit einem Absolutdruck von 10- 60
mmHg eingeführt wird, daß das Material von Schritt c) mit einem Transportmittel durch
die Vakuumkammer geführt wird, und daß das getrocknete Material optional grob zerkleinert
wird, bevor es über eine Luftschleuse im Schritt d) aus der Vakuumkammer entfernt
wird.
3. Verwendung nach Anspruch 2, dadurch gekennzeichnet, daß die Geschwindigkeit des Transportmittels
einstellbar ist.
4. Verwendung nach Anspruch 1, dadurch gekennzeichnet, daß die Temperatur des Materials
im Schritt a) auf eine Temperatur von weniger als 30° unterhalb des Siedepunkts des
Materials eingestellt wird, vorzugsweise weniger als 10° unter dem Siedepunkt, daß
das Material im Schritt b) in eine Vakuumkammer mit einem Absolutdruck von 10- 60
mmHG eingeführt wird, daß das Material im Schritt c) im freien Fall durch die Vakuumkammer
geführt wird, und daß das getrocknete Material optional grob zerkleinert wird, bevor
es über eine Luftschleuse im Schritt d) aus der Vakuumkammer entfernt wird.
5. Verwendung nach Anspruch 1, dadurch gekennzeichnet, daß das in die Vakuumkammer eingeführte
Material ein Trockensubstanzgehalt von 91 bis 95 Gewichtsprozent aufweist.
1. Utilisation d'un procédé pour le séchage en continu d'une matière, selon laquelle
a) la température de la matière est ajustée à une valeur qui n'est pas préjudiciable à la matière,
b) la matière est introduite dans une chambre à vide,
c) la matière est acheminée à travers la chambre à vide sans aucun apport de chaleur à la matière, et
d) la matière séchée est retirée de la chambre à vide en passant par sas à air ;
caractérisée en ce que la matière est un sirop sensiblement exempt de particules, choisi dans le groupe formé par les sirops de glucide et les sirops d'alcool de sucre, et en ce que la température dudit sirop dans l'étape a) est ajustée à une valeur inférieure au point d'ébullition de ladite matière à la pression atmosphérique, mais suffisamment élevée pour que la matière soit séchée dans l'étape c) en un produit solide amorphe.2. Utilisation selon la revendication 1, caractérisée en ce que la température de la
matière dans l'étape a) est ajustée à une valeur inférieure de moins de 30°C au point
d'ébullition de la matière, de préférence inférieure de moins de 10°C au point d'ébullition,
en ce que la matière dans l'étape b) est introduite dans une chambre à vide où règne
une pression absolue de 10 à 60 mm de Hg, en ce que la matière de l'étape c) est acheminée
à travers la chambre à vide par un moyen de transport et en ce que la matière séchée
est facultativement broyée grossièrement avant d'être retirée de la chambre à vide
en passant par sas à air dans l'étape d).
3. Utilisation selon la revendication 2, caractérisée en ce que la vitesse du moyen de
transport est réglable.
4. Utilisation selon la revendication 1, caractérisée en ce que la température de la
matière dans l'étape a) est ajustée à une valeur inférieure de moins de 30°C au point
d'ébullition de la matière, de préférence inférieure de moins de 10°C au point d'ébullition,
en ce que la matière dans l'étape b) est introduite dans une chambre à vide où règne
une pression absolue de 10 à 60 mm de Hg, en ce que la matière dans l'étape c) est
acheminée à travers la chambre à vide par chute libre et en ce que la matière séchée
est facultativement broyée grossièrement avant d'être retirée de la chambre à vide
en passant par sas à air dans l'étape d).
5. Utilisation selon la revendication 1, caractérisée en ce que la matière introduite
dans la chambre à vide a une teneur en matière sèche de 91 à 95 % en poids.